The present invention relates to a carriage pre-load support and bushing system for a large scale computer driven plotter carriage which slides back and forth transversely of the path of paper travel through the plotter on a pair of smooth support rods which are ordinarily cylindrical.
Carriage bushing systems require high tolerance and low friction and have inherently conflicting design requirements since high tolerance bushing systems require dimensionally stable materials which usually have high coefficients of friction. Conversely, a bushing system which is constructed primarily of lubricous material for reduced friction tends to be dimensionally unstable. The problem is compounded with increasing size of the printer or plotter. Low friction bushings can be manufactured to the required tolerances by secondary machining operations with repeated inspections and rejection of bushings that are not manufactured to the correct tolerance. Clearly, such operations materially increase the per part finished cost.
A carriage support system which can be manufactured to and retain close tolerances is therefore required for large scale plotter carriages such as for drafting plotters which must move without impediment at a high rate of speed with frequent reversals in the direction of movement along the slider rods.